Chem 3A Problem 5 : The ionization constant for water ( K w) is 2.9 × 10–14 at 4

Question

Chem 3A

Problem 5: The ionization constant for water (Kw) is 2.9 × 10–14 at 40 °C. Calculate 3 [H O+ ],

[OH–], pH, and pOH for pure water at 40 °C.

Problem 6: Calculate the pH and the pOH of each of the following solutions at 25 °C for which

the substances ionize completely:

(a) 0.200 M HCl

(b) 0.0143 M NaOH

(c) 3.0 M HNO3

(d) 0.0031 M Ca(OH)2

Problem 7: What are the pH and pOH of a solution of 2.0 M HCl, which ionizes completely?

Problem 8: What are the hydronium and hydroxide ion concentrations in a solution whose pH is

6.52?

Problem 9: The hydronium ion concentration in a sample of rainwater is found to be 1.7 × 10–6

M at 25 °C. What is the concentration of hydroxide ions in the rainwater?

Problem 10: The hydroxide ion concentration in household ammonia is 3.2 × 10–3 M at 25 °C.

What is the concentration of hydronium ions in the solution?

Explanation / Answer

5)

H2O + H2O   <—> H3O+(aq)   +   OH-(aq)

for pure water,

[H3O+] = [OH-]

Kw = [H3O+] [OH-]

2.9*10^-14 = [H3O+][H3O+]

2.9*10^-14 = [H3O+]^2

[H3O+] = 1.703*10^-7 M

[OH-] = [H3O+] = 1.703*10^-7 M

pH = -log [H3O+]

= -log (1.703*10^-7)

= 6.77

pOH = -log [OH-]

= -log (1.703*10^-7)

= 6.77

I am allowed to answer only 1 question at a time

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